Call --mbrtogpt on journal run of sgdisk should the drive require a GPT table.

Signed-off-by: Jonathan Davies <jonathan.davies@canonical.com>
Reviewed-by: Sage Weil <sage@inktank.com>
Reviewed-by: Loic Dachary <loic@dachary.org>
Merge pull request #892 from jpds/ceph-disk-journal-mbrtogpt

Call --mbrtogpt on journal run of sgdisk should the drive require a GPT ...

Reviewed-by: Sage Weil <sage@inktank.com>
Reviewed-by: Loic Dachary <loic@dachary.org>